>I don't understand how organisms with radial symmetry can have crossed
>representation
they don't... what I said in my original post was that the overall
phenomenon can be traced back to organisms having radial symmetry...
...the highly-inefficient radial-symmetry "correlate" of decussation
exists in the spread of activation through the radial net... one
observes the net's response to stimuli... the outward appearance is
somewhat like the gradual deformation of, say, an orange, the juice of
which is being sucked out through a hole poked through the orange's
skin... such is a topological inversion of the topology of the
phenomenon of decussation... to communicate with "the orher side of the
circle", radially-symmetric organisms just pass activation around the
circumference... this leisurely rate of signalling allows only
relatively slow whole-organism coordinated motion...
...it's in this sense that the phenomenon can be traced back to
organisms having radial symmetry... the inefficiency of the
radial-symmetry topology exposes the need for decussation... ken